A method of designing a 3D Integrated Circuit, the method including: partitioning at least one design into at least two levels, a first level and a second level; providing placement data of the second level; performing a placement of the first level using a placer executed by a computer, where the placement of the first level is based on the placement data, where the placer is part of a Computer Aided Design (CAD) tool, and where the first level includes first routing layers; and performing a routing of the first level by routing layers using a router executed by a computer, where the router is a part of the Computer Aided Design (CAD) tool or a part of another CAD tool.